In Greek mythology, Cerberus traditionally had three heads when Hercules captured him.
Cerberus was the monstrous watchdog of Hades, the underworld. He prevented the dead from leaving and the living from entering. In the final labor, Eurystheus ordered Hercules to bring the dog to the surface without using weapons.
Hercules obtained permission from Hades and Persephone before taking Cerberus away. Ancient accounts describe him overpowering or restraining the dog while protected by his lion skin and strength. He then displayed Cerberus to Eurystheus before returning the creature to the underworld.
Although the three-headed form is the best-known version, descriptions of Cerberus vary. Some ancient representations give him additional animal features, such as snakes around his neck or a serpent for a tail. These variations do not change the standard trivia answer of three heads.